The source told Reuters the Gulf-financed shipment, which came from the Turkish province of Hatay in the past 24 hours, was one of the single biggest shipments of weapons to reach rebel forces since the uprising against President Bashar Assad turned deadly more than two years ago.

"Twenty trailers crossed from Turkey and are being distributed to arms depots for several brigades across the north," Mohammad Salam, a rebel operative who witnessed the crossing from an undisclosed location in Hatay, told Reuters.

A senior official in the Gulf and Western backed Supreme Military Council, an umbrella group for rebel troops, confirmed the arms delivery, and said that weapons airlifts into Turkey have significantly increased since rebel held Sunni neighbourhoods and suburbs of the Syrian capital Damascus were allegedly gassed last Wednesday.

Iran's foreign minister said the Syrian government had told Tehran it would allow U.N. inspectors to visit areas reportedly affected by chemical weapons, Iran's Press TV said on Sunday, according to Reuters. This follows hints made by Syrian minister of information Omran Zoabi that the UN team, already in Damascus, would not be allowed access to the chemical weapons site as it was not previously agreed on by the UN and the Syrian government.